This invention relates to a toner density controlling device for automatically controlling the toner density of a developing agent in an electronic copying apparatus which uses a developing agent in the form of powder consisting of two components, namely, toner and carrier.
A variety of toner density controlling devices of this type in which the percentage content of toner in a developing agent is optically or electrically detected to provide a detection signal, which is utilized to automatically supply toner, have been proposed in the art.
For instance,
(1) In a first example of a conventional density controlling device, the color density variation of the toner in the developing agent is measured to provide an output signal, which is utilized to control the supply of toner,
(2) In a second example, the electrical conductivity of the developing agent is measured to provide an output signal, which is utilized to control the supply of toner,
(3) In a third example, the specific gravity of the developing agent is measured to provide an output signal, which is utilized to control the supply of toner, and
(4) In a fourth example, the variation in a physical characteristic of the developing agent due to a difference in the percentage content of toner, such as for instance the fluidity of the developing agent, is measured to provide an output signal, which is utilized to control the supply of toner.
In the case of example (1), the color density variation of toner is small, and accordingly the accuracy is low. In the case of the second example, the electrical conductivity of the developing agent is small, and accordingly the noise is large. In example (3), it is necessary to perform weight and volume measurements in the copying machine; however, the measurements are low in accuracy because they are liable to be affected by vibration. In the case of the fourth example, the measurement is also liable to be affected by vibration, and the accuracy is therefore low.
As is apparent from the above description, the conventional density controlling devices suffer from difficulties in that the accuracy thereof is low, for example.